Hydrolysis of Dietary Lipids
Dietary lipids are an important source of energy. The energy-rich triacylglycerols constitute more than 95% of these lipids. Some of the lipids, e.g. certain fatty acids and the fat-soluble vitamins, are essential dietary constituents. Before gastro-intestinal absorption the triacylglycerols as well as the minor components, i.e. esterified fat-soluble vitamins and cholesterol, and diacylphosphatidylglycerols, require hydrolysis of the ester bonds to give rise to less hydrophobic, absorbable products. These reactions are catalyzed by a specific group of enzymes called lipases.
In the human adult the essential lipases involved are considered to be Gastric Lipase, Pancreatic Colipase-Dependent Lipase (hydrolysis of tri- and diacylglycerols), Pancreatic Phospholipase A2 (hydrolysis of diacylphosphatidylglycerols) and Carboxylic Ester Lipase (CEL) (hydrolysis of cholesteryl- and fat soluble vitamin esters). In the breast-fed newborn, Bile Salt-Stimulated Lipase (BSSL) plays an essential part in the hydrolysis of several of the above mentioned lipids. Together with bile salts the products of lipid digestion form mixed micelles from which absorption occurs.